# std::ranges::in_out_out_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
template< class I, class O1, class O2 > struct in_out_out_result; |  | (since C++20)

`ranges::in_out_out_result` is a class template that provides a way to store three iterators as a single unit.

This class template has no base classes or declared members other than those shown below. Thus it is suitable for use with structured bindings.

All special member functions of this class template are implicitly declared, which makes specializations be aggregate classes, and propagate triviality, potentially-throwing-ness, and constexpr-ness of corresponding operations on data members.

### Template parameters

I, O1, O2 | - | the types of the objects that the `ranges::in_out_out_result` stores.

### Data members

Member name | Definition
in | a value (that is supposed to be an iterator) of type `I`. (public member object)
out1 | a value (that is supposed to be an iterator) of type `O1`. (public member object)
out2 | a value (that is supposed to be an iterator) of type `O2`. (public member object)

All these members are declared with `[[no_unique_address]]` attribute.

### Member functions

## std::ranges::in_out_out_result::operator in_out_out_result<II, OO1, OO2>

template<class II, class OO1, class OO2> requires std::convertible_to<const I&, II> && std::convertible_to<const O1&, OO1> && std::convertible_to<const O2&, OO2> constexpr operator in_out_out_result<II, OO1, OO2>() const &; | (1) |
template<class II, class OO1, class OO2> requires std::convertible_to<I, II> && std::convertible_to<O1, OO1> && std::convertible_to<O2, OO2> constexpr operator in_out_out_result<II, OO1, OO2>() &&; | (2) |

Converts *this to the result by constructing every data member of the result from the corresponding member of *this.

1) Equivalent to return {in, out1, out2};.
2) Equivalent to return {std::move(in), std::move(out1), std::move(out2)};.

### Standard library

The following standard library functions use `ranges::in_out_out_result` as the return type:

##### Algorithm functions
ranges::partition_copy (C++20) | copies a range dividing the elements into two groups (algorithm function object)

### Synopsis

    namespace std::ranges
    {
        template<class I, class O1, class O2>
        struct in_out_out_result
        {
            [[no_unique_address]] I  in;
            [[no_unique_address]] O1 out1;
            [[no_unique_address]] O2 out2;

            template<class II, class OO1, class OO2>
            requires std::convertible_to<const I&, II> &&
                     std::convertible_to<const O1&, OO1> &&
                     std::convertible_to<const O2&, OO2>
            constexpr operator in_out_out_result<II, OO1, OO2>() const &
            {
                return {in, out1, out2};
            }

            template<class II, class OO1, class OO2>
            requires std::convertible_to<I, II> &&
                     std::convertible_to<O1, OO1> &&
                     std::convertible_to<O2, OO2>
            constexpr operator in_out_out_result<II, OO1, OO2>() &&
            {
                return {std::move(in), std::move(out1), std::move(out2)};
            }
        };
    }

### Notes

Each standard library algorithm that uses this family of return types declares a new alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.

The names for such aliases are formed by adding the suffix "`_result`" to the algorithm's name. So, the return type of `std::ranges::merge` can be named as `std::ranges::merge_result`.

Unlike std::pair and std::tuple, this class template has data members of meaningful names.

### Example

Run this code

    #include <algorithm>
    #include <array>
    #include <cctype>
    #include <iostream>
    #include <iterator>
    #include <ranges>
    #include <string_view>

    void print(std::string_view rem, auto first, auto last)
    {
        for (std::cout << rem << ": { "; first != last; ++first)
            std::cout << *first << ' ';
        std::cout << "}\n";
    }

    int main()
    {
        constexpr std::string_view in {"TvEeNcStOoRr"};
        std::array<char, in.size()> o1, o2;

        const auto result = std::ranges::partition_copy(in, o1.begin(), o2.begin(),
            [](char c) { return std::isupper(c); });

        print("in", in.begin(), result.in);
        print("o1", o1.begin(), result.out1);
        print("o2", o2.begin(), result.out2);
    }

Output:

    in: { T v E e N c S t O o R r }
    o1: { T E N S O R }
    o2: { v e c t o r }

### See also

pair | implements binary tuple, i.e. a pair of values (class template)
tuple (C++11) | implements fixed size container, which holds elements of possibly different types (class template)

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